Aug. 26,V 1958
M. T. wr-:lss
29849’685
NON-RECIPROCAL MULTIBRANCH WAVE- GUIDE COMPONENT
Filed Aug. 17, 1953'
3 Sheets-Sheet l
FIG. /
//\
A4* .Est4ima
.
)Nl/Enron
M ZrWE/SS
ATTORNEY
Aug. Z6, 1958
2,849,685
M. T. WEISS
NON-RECIPROCAL MULTIBRANCH WAVE GÚIDE COMPONENT
Filed Aug. 17. 1953
5 Sheets-Sheet 2
85
l .
\
REcE/VER
„TRANSMITTER
8/
/A/l/EA/TOR
BV
M. 7T WEISS
,MIZ J.
A 7` TORNEV
Aug. 26, 195s
M. T. WEISS
2,849,685
NON-RECIPROCAL MULTIBRANCH WAVE GUIDE COMPONENT
Flled Aug. 17, 1955
l
\'\/
i
i
|./
‘N
-
I
l
‘\‘<
L
œ
4
United States Patent O M1C@
2,849,685
Patented Aug. 26, 1958
2
NON-RECIPROCAL MULTIBRANCH WAVE GUmE
COMPONENT
Max T. Weiss, Red Bank, N. J., assignor to Bell Tele
phone Laboratories, Incorporated, NewI York, N. Y.,
a corporation of New York
are provided with spaced groups of apertures through
the common wall and with transversely biased ferromag
netic elements in one or both of the guides between the
groups of apertures. With the groups of apertures being
of the directional coupler type and the transversely biased
ferromagnetic elements providing non-reciprocal phase
shift, the result is a simple, compact nonreciprocal multi
branch circuit having excellent stability of operation
over a broad range of frequencies and temperatures.
Application August 17, 1953, Serial No. 374,511
In the prior art nonreciprocal multibranch waveguide
circuits, the coupling structures are relatively inflexible
11 Claims. (Cl. S33-10)
and can only couple energy in its entirety from one ter
minal to another. This is a result of the standardized
The present invention relates to multibranch wave
guide components which have nonreciprocal properties.
The so-called “Theorem of Reciprocity” states that:
“In any network composed of linear impedances, if
an electromotive force E applied between two terminals
nature of the sub-component hybrid junctions which have
been employed in these structures.
Another advantage of the present invention lies in its
applicability to microwave systems requiring nonrecipro
cal' power splitting as well as to waveguide coupling ar
energy applied at a lirst terminal appears at a second
rangements in which the input power is coupled in its
This feature, which
results from the use of directional coupling apertures of
a particular conñguration, is particularly useful in muti
ple antennae wave-transmission systems.
Other objects, features and advantages will be de
veloped in the course of the detailed description of the
drawings, in which:
terminal, then energy applied to this second terminal
would appear at the first terminal. In nonreciprocal
phase shifter;
produces a current I at some branch in the network, 20 entirety to a single output terminal.
then the same voltage E acting at the second point in
the circuit, will produce the same current I at the first
point.”
As applied to a waveguide unit having three or more
terminals, this theorem indicates that if electromagnetic
multibranch waveguide circuits, however, these relation
ships do not hold and energy applied at the second termi
nal might appear at still another terminal, or the energy
could be split between the first terminal and another ter-
minal.
Nonreciprocal multibranch waveguide compo
nents can be used for many purposes including, for ex
Fig. l is a cross-sectional view of a nonreciprocal
Fig. 2 is a cut away isometric View of a rectangular
waveguide circulator in accordance with the invention;
Fig. 3 is a cross-sectional view of the device of Fig. 2
taken along line 3_3 of that figure;
Fig. 4 is a schematic representation of the circulator
of Figs. 2 and 3;
ample, the coupling of both a transmitter and a receiver 35
Fig. 5 shows an alternative circulator in which two 90
to a single antenna. In such an arrangement, energy
degree phase shifting elements are employed instead of
from the transmitter is coupled in its entirety to the
antenna and simultaneously energy received at the an
tenna is coupled solely to the receiver.
It has previously been proposed to construct a non 40
reciprocal multibranch circuit employing magic tee hy
brid junctions and a Faraday rotation nonreciprocal ele
ment (see C. L. Hogan’s article “The microwave gyra
tor,” Bell System Technical Iournal, volume 3l, I anuary
1952, pages l-31).
However, such a structure is some
the single 180 degree phase shifter shown in Figs. 2
through 4;
Fig. 6 is an isometric representation of a broadband
circulator;
Fig. 7 is a schematic diagram of the device of Fig. 6;
Fig. S shows a nonreciprocal multibranch coupler in
a waveguide circuit; and
Fig. 9 represents a circulator having excellent sta
bility o-f operation.
Referring more particularly to the drawings, Fig. l
what cumbersome and bulky, as it involves the mutually
orthogonal arms of the magic tee, the rectangular to
shows a hollow waveguide 1l having an element of ferro
round transitions and the large magnet of the Faraday
magnetic rnaterial 12 located therein. When this ferro
effect rotator, and the necessary waveguide fittings to
magnetic element, which may be, lfor example, a poly
50 crystalline ferrite element, is transversely magnetized as
interconnect the foregoing elements.
Accordingly, a principal object of the present inven
indicated by the arrow H in Fig. l, the phase shift for
one direction of propagation through the waveguide ll
tion is to simplify nonreciprocal multibranch circuits.
A known nonreciprocal multibranch circuit of the prior
is greater than for the opposite direction of propa
art has employed a single pencil of ferromagnetic ma
gation. This phenomenon is now well known and is
discussed in greater detail in S. E. Miller application
terial mounted in dielectric as the non-reciprocal element. t
Although this type of device operated satisfactorily at
Serial No. 362,193, filed lune 17, i953. The ferrite ele
ment i2 is located asyrnmetrically in the waveguide and
relatively low power levels and at a given frequency,
is preferably spaced from the side wail but by a distance
changes in ambient temperature at high power levels or
other changes in operating conditions severely impaired
the operating qualities of the units.
not greater than one-quarter of the distance across the
waveguide. As the length of the septum 12 is increased,
A collateral object is to reduce the adverse eiîect of
temperature, frequency or other deviations on the oper
the arno-unt of the difference in phase shift for the two
ating qualities of a non-reciprocal multibranch waveguide
At the critical length of the ferrite septum, the difference
in phase shift for the two directions of propagation is
exactly 180 degrees as set forth in greater detail in the
above-noted S. E. Miller application. A device which
has 180 degrees difference in phase shift for the two
directions of propagation has been termed a gyrator
While the structure of Fig. l is perhaps the simplest
component.
`
In accordance with the invention, a nonreciprocai
multibranch waveguide component is made up of. two
adjacent waveguides which have appropriate coupling
along their lengths and at least one non-reciprocal phase
shifting element associated with one of the waveguides.
More specifically and in accordance with one illustrative
embodiment of the invention discussed in detail herein
ßflôr, two rectangular waveguides having a common wall
directions of propagation is correspondingly increased.
nonreciprocal phase shifting arrangement for rectangular
waveguides, other conñgurations of ferromagnetic ma
terial and steady transverse magnetic field will also pro
2,849,685
3
,4
duce this result. For example, referring to Fig. 1, the non
reciprocal effect would be enhanced if another element
of ferrite biased in the upward direction were placed ad
jacent the left-hand narrow side wall of the waveguide 11.
wave at point 41 will be 90 degrees displaced in phase
from that at point 42.
The symbols nk and n’À represent reciprocal phase
shifts required to obtain a convenient length between the
apertures 26 and 27. Therefore, at point 43 just before
the aperture 27, the energy in the waveguide 22 will have
been shifted by 90 degrees plus nk reciprocal phase shift,
When the waveguide is ñlled with ferrite and an asym
metric transversemagnetic ñeld applied thereto, a simi
lar result obtains. In addition it may be noted that the
transverse magnetic ñeld may be supplied by an external
magnetic ñeld from a permanent magnet or an electro
magnet, or by permanently magnetizing the ferromagnetic
septum itself.
while the energy at the comparable point 44 of wave
guide 21 will be shifted by 180 degrees plus n’ìt recipro
cal phase shift.
Inasmuch as 11A and n’k are equal or
Still other alternative structures and an
dillcr by an integral number of full wavelengths, these
analysis of their operation may be found in the above
identified application of S. E. Miller.
Figs. 2 through 4 represent a nonreciprocal multi
branch waveguide circuit in accordance with the inven
tion which makes use of nonreciprocal phase shifting elc
ments of the type disclosed in Fig. l. Fig, 2 shows
phase shifts may be ignored. At the second directional
coupling aperture 27 the power again splits with one
half of the energy in each waveguide being coupled to
the opposite waveguide. More explicitly, when each of
two parallel waveguides 21 and 22 which have a common
narrow wall 23. In the waveguide 21 is a transversely
the two .707 amplitude waves are split, the result is two
waves each having a voltage amplitude equal to .5 that
of the original coherent source. The energy which passes
from the waveguide 21 to the waveguide 22 will undergo
biased ferromagnetic septum 24 having 180 degrees dif 20 another 90 degree shift and thus will be in 180 degree
ference in phase shift for the two directions of transmis
sion through waveguide 21. A dielectric counterpoise 25
is located in waveguide 22 and is the same size and shape
as the ferrite element 24. In addition, these two elements
are symmetrically located with respect to the plane of
the common wall 23 between the two waveguides. It is,
however, not necessary that the counterpoise be ofiexact
ly the same form as the ferrite element, as long as it has
substantially the same effective electrical length. Before
phase opposition to the portion of the energy in wave
guide 22 which is not coupled back to the waveguide 21.
and thus the two wave forms will completely cancel each
other out. The energy from waveguide 22 which is
coupled over to waveguide 21 will also undergo another
90 degree phase shift. and this will place it in phase with
the energy in waveguide 21 and they will combine to give
unity output at terminal B. By a similar procedure it
can readily be developed that energy applied at terminal B
and after the ferrite plate and the dielectric counterpoise 30 will appear only at terminal C, ctc., as set forth herein
before.
In the schematic diagram ot' Fig. 4 the slots 26 and 27
the common wall 23 is apertured. These apertures 26
and 27 are of a type known as directional couplers and
are described in articles by S. E. Miller and W. W. Mum
have arrows and the indication sin 45 degrees associated
ford in the Proceedings of the Institute of Radio Engi
therewith. This indicates the amplitude of coupling
neers, volume 40, pages 1071-1078, September 1952, and 35 (.707 amplitude) between the two guides. The product
by H. J. Riblet in the Proceedings of the Institute of
of the amplitude coupling per unit length times the length
Radio Engineers, volume 40, pages 180-184, February
1952.
Fig. 3 is a cross-sectional view along lines 3_3 of
Fig. 2 and also shows the magnetic structure for magneti
cally polarizing the ferrite element. As shown in this
view the biasing field for the ferrite septum 24 may be
supplied by the electromagnet made up of the core 31
and the coil 32 energized by a suitable source of electric
voltage 33 controlled by the variable resistance 34.
The operation of the nonreciprocal multibranch cir
cuit may be more readily described with reference to Fig.
4 which is a schematic view of this device. In this ñgure
it may be noted that the ferrite plate 24 is shown as a
box with the Greek letter 1r and an arrow therein to
indicate that this section of waveguide has 180 degrees
more phase shift for transmission from left to right in
of the directional coupling apertures may be expressed as
an angle and the coupling would then be proportionate to
the sin of this angle. Full coupling is obtained if the
sum of these angles is 90 degrees. Reference is made
to the above-cited Miller-Mumford article for further
details of this method of analysis.
The alternative arrangement of Fig. 5 shows two wave
guides 51 and 52 having a common wall 53 and two
_ spaced 3 db coupling apertures 54 and 55. Instead of
the single 180 degrees nonreciprocal phase shift element
employed in the device of Figs. 2 to 4, two 90 degree
phase shifting elements 56 and 57, one in each of wave
guides 51 and 52 are used in this structure of Fig. 5.
However, as indicated by the symbol
A
the direction of the arrow than for the opposite direc
4
tion of propagation. The directional coupling apertures
under the element 56 the effective electrical length of
26 and 27 have the property that energy transmitted from
the waveguide 52 between coupling apertures must now
terminal A will be split at the aperture 26 and will travel
be a quarter wavelength greater than the comparable
toward terminals B and D but no energy will be coupled
section of waveguide 51. With this arrangement, the
to terminal C. This property of directional couplers is
same circulator action is again obtained, with energy
developed in detail in the above-noted article by W. W.
passing from terminal A to terminal B, B to C, C to D,
Mumford and S. E. Miller.
Using two 3 db (.707 amplitude) coupling apertures at 60 and from D to terminal A, just as in the device of Figs.
2 through 4.
26 and 27 it can be rigorously shown that energy ap
In Figs. 6 and 7 an improved version of the circulator
plied at terminal A appears at terminal B; energy applied
is illustrated. In this case guides 61 and 62 have the
at terminal B appears at terminal C (not, as might be
usual common wall 63 and are provided with three
expected, at terminal A), energy applied to terminal C
appears at terminal D, and finally, energy applied at ter 65 coupling apertures 64, 65 and 66 and two gyrator ele
minal D appears at terminal A.
To see the physical reason why no energy applied at
terminal A appears at terminal D, for example, the volt
ments 67 and 68.
In this instance the directional cou
pling structures are of a broad band type such as are
disclosed in the article by S. E. Miller and W. W. Mum
age amplitude and phase shift at various points through
ford in the proceedings of the Institute of Radio Engi
the waveguide structure must be traced. Starting with 70 neers, volume 40, pages l071-1078, September 1952.
units voltage applied at terminal A the coupler 26 splits
By employing an additional nonreciprocal 180 degree
the power equally so that the peak voltage at point 41 and
phase shift section it will be shown that any change in‘
at point 42 is .707 of unity. The directional coupler
the value of this phase shift, due to factors such as'
structure 26 has the property of shifting the phase of
temperature or frequency variations, which affect both
wave energy passing through it by 90 degrees so the 75 phase shift sections equally, is cancelled out to the ñrst'
2,849,685
5
6
order. As contrasted with the circulators of Figs. l
through 5, the structures of Figs. 6 and 7 show that for
the cost of broad band coupling apertures and an extra
180 degree nonreciprocal section the overall stability of
the device is greatly improved. In passing, it may be
noted that the amplitude coupling lof the slots 64, 65
and 66 are equal to sine 22.5 degrees, sine 45 degrees,
and sine 22.5 degrees respectively. Because these angles
add up to 90 degrees, this structure is a true circulator,
and full coupling may be expected.
The device indicated schematically in Fig. 8 is a non
reciprocal multibranch coupling circuit which is not a
true circulator.
.
which is equal to +(1‘A)"»+ higher order terms since
1 _nein _plivâëßem _”(lflll’äëïg.) Ginn., +
(-1)" 1.2.3.„n
"Mälümnzqmw
higher order terms
Therefore we can solve the equation for 0 so as to
obtain the binomial relation. The result is, after some
trigonometric substitutions,
2 sin2 20+2 sin 20-1=0
In this arrangement, the sum of the
angles associated with the coupling slots only add up
to 45 degrees, and therefore only part of the power is
and
coupled over in a non~reciprocal manner. Thus, for
example, power from the transmitter 81 is transmitted
through the waveguide section 82 to two dilîerently
oriented antennae 83 and 84. Power picked up by the
and
antenna 83, however, goes only to the receiver 85. The 20
multibranch coupling circuit which makes this possible
includes the usual parallel waveguides 86 and 87, the
directional coupling apertures 88 and 89 through the
or sin 20:.366025
26=21.466°
0=10.73°
2¢=68.534°
¢=34.27°
With this design the unwanted output at II with input
at III will therefore be proportional to (jA)3 which is,
of course, much smaller than for the single section cir
common wall 90, and the gyrator element 91. The
coupled apertures in the present instance, however, are 25 culator for which the output at II is proportional to J'A.
The above scheme can =be used for designing an n sec
8.32. db (.383 amplitude) couplers and hence only one
tion circulator which will be compensated for changes
half of the power is coupled across to the other wave
guide in the entire coupling structure.
in the?? phase Shift te (jaw.
The circulator of Fig. 9 is patterned after the struc
Concerning the materials used in the nonreciprocal
tures of Figs. l through 8 but has an additional gyrator
phase shifting elements, they can be made from any suit
section, and hence has an even higher order of stability
able ferromagnetic material of low conductivity. When
than the circulator of Figs. 6 and 7. Structurally, the
the term “low conductivity” is employed in the present
circulator has two parallel waveguides 71 and 72 having
speciñcation and claims it means that the material in
a common wall ’73 which in turn has four sets of di
question has an overall resistivity of 10 to 100 ohm
35
rectional coupling slots 74 through 77. In each of the
centimeters or more. While polycrystalline ferrites are
intervals between the coupling slots gyrator elements 81,
preferred, the phase shifting effect has been observed in
S2 and 83 are located.
other materials such as very finely divided iron particles
The exact manner of splitting the coupling between
in an insulating dielectric matrix. In regard to the struc
the various directional coupler slots can be calculated
ture
of nonreciprocal phase shifting elements in each of
in the manner shown by the following example for the 40 the figures of the drawing, these may be of any known
three section circulator of Fig. 9.
type, and specifically may be of any of the forms disclosed
The amplitude coupling in the first and last sections
in conjunction with Figs. 1 through 4. For a more
is equal to sin 0, while the two middle sections each
thorough treatment of these phase shifting phenomena,
have a coupling equal to sin (p. In order that com
reference is again made to the application of S. E. Miller,
plete coupling take place in the desired direction, 20+2<p 45 Serial No. 362,193 which is 4assigned to the assignee of
must equal 90 degrees.
the present invention
From the above it follows that cos 20=sin 2<p and
It is to be understood that the above-described ar
rangements are illustrative of the application of the
sin 20=cos 2e. Let us assume that all the Tr) sections
have a phase shift `of vr-i-A. With an input of unit 50 principles of the invention. Numerous other arrange
ments may be devised by those skilled in the art without
amplitude at III, let us calculate the output at II. The
following table shows how one proceeds, taking into
account only differences in phase shift between top and
bottom guides:
Table I
Upper
guide.
Lower
guide.
departing from the spirit and scope of the invention.
What is claimed is:
l. In combination, a first and a second substantially
parallel rectangular waveguide for electromagnetic wave
55 energy having a common wall therebetween, "n” spaced
At a
At b
At c
At d
1
cos 6
cos 9
cos 0 cos ¢+sin 6 sin peiA
0
j sin 6
-j sin H eiA
[-j sin 6 cos e eiA-t-j sin q: cos 0]
directional coupling apertures through said common wall
where n is greater than two, means including elements
of gyromagnetic material magnetized transversely to said
common wall interposed between said coupling apertures
in at least one of said waveguides for shifting the phase
of wave energy in `said first waveguides with respect to
wave energy propagating in said second waveguide bya
and so on until we reach the output at II. This is
phase angle in one direction of x degrees, said phase shift
given by
being nonreciprocal for shifting the phase of wave energy
65 propagating in said first waveguide with respect to Wave
energy propagating in said second path in the reverse di
'
sin20 sin o cos e-cos 0 sin 0 sin2q5][e1'^--ef2A]
rection by a Value of [x-(n-l)(l80)] degrees.
which we want to equal 0 i-i- terms in A3 and higher so
2. A combination as defined in claim 1 wherein said
as to depart from 0 at a minimum rate. We thus have
apertures are of such a conüguration that there is an un
an equation which we shall write for simplicity as
70 equal division of power at one of said directional coupling
A _BeiA+Cei2A+Defs/i
lt is well known that if A, B, C, D form a binomial
relation, 'then the above equation will lbe equal to
apertures.
3. In a stable nonreciprocal multibranch waveguide
component, two waveguides having longitudinally extend
ing axes, three spaced regions of coupling between said
75 two waveguides, and an element -of gyromagnetic material
2,849,685
7
8
coupled to one of said waveguides and confined in each
of the intervals between each of said coupling regions,
four-branch power dividing networks, each of said
branches having the branches thereof arranged in pairs
with the branches comprising one pair being conjugate
said elements being magnetically biased transversely to
the axis of said one waveguide.
4. In combination, two substantially parallel rectangu
lar waveguides having a common wall, three spaced
to each other and in coupling relation to the branches of
the other pair, at least one of said networks being of
directional lcoupler type introducing a 90-degree phase
broadband directional coupling slots in said common wall,
and nonreciprocal phase shifting elements coupled to one
shift to wave _energy coupledbetween said pairs, a first
wave transmission path connecting a branch of one pair
of said waveguides in each of the intervals between said
directional coupling slots.
5. In a nonreciprocal multibranch waveguide compo
of branches of said first network to a branch of one pair
10 of branches of said second network, a second wave trans
mission path separate from said iirst path connecting
nent, two substantially parallel rectangular waveguides
having longitudinally extending axes, a plurality of spaced
the other branch of said one pair of said first network to
the other branch of said one pair of said second network,
directional coupling means for transferring a fraction of
means including an element of gyromagnetic material
the energy in one of said waveguides to the other wave
interposed in both 0f said paths and magnetized trans
guide, at least one of said coupling means transferring
versely to the axes of said paths for shifting the phase of
a fraction not greater than sine _22.5 degrees and at least
wave energy in said Íirst path with respect to the phase
one paramagnetic element of low conductivity coupled to
shift introduced to wave energy in said second path by
at least one of said guides in »the interval between each
a phase angle for propagation in one direction along said
pair of said directional coupling means, said element 20 paths of x degrees, said phase shift being non-reciprocal
being magnetized transversely to the axes of said guides.
and capable at‘ the same time of shifting the phase of
6. A waveguide component as set forth in claim 5
wherein there are at least three directional coupling means.
7. A waveguide component as set forth in claim 5
wherein there are two directional coupling means each of 25
which is >approximately 8.34 decibel couplers.
8. In combination, two waveguides having longitudi
nally extending axes, two spaced directional couplers in
terconnecting said waveguides, each of said couplers con
stituting means for transferring a minor fraction of the 30
power in one of said waveguides to the other, said minor
fraction being no greater than -834 decibels of .the
total power applied to said one waveguide, and `nonre
ciprocal phase-shifting means coupled to at least one of
said waveguides between said spaced couplers.`
35
»9. A nonreciproeal power-splitting waveguide compo
nent in accordance :with claim 8 wherein each coupling
structure is approximately an 8.34 decibel coupler and
wave energy propagating in va direction opposite to said
one direction in said first path with respect to the phase
shift introduced to wave energy propagating in said op
posite direction in said second path by a value of x-180
degrees.
References jCited in the tile of this patent
UNITED STATES PATENTS
2,593,120
Dicke ________________ __ Apr. 15, 1952
2,629,079
Miller ______________ __ Feb. 17, 1953
2,671,884
2,679,631
29,728,050
2,745,069
ZaleSki _____________ __ Mar. 9,
Korman _____________ __ May 25,
Vanl de Lindt _________ __ Dec. 20,
Hewitt ______________ __ May 8,
Hogan ______________ __ May 29,
2,748,353
1954
1954
1955
1956
1956
OTHER REFERENCES
the entire unit divides the power input at one of the four
Publication, Riblet: “The Short Slot Hybrid Junction,”
terminals into two substantially equal parts.
. 40 Proceedings of the I. R. E., vol. 40, No. 2, February 1952,
pp. 180-184.
.110. A combination as set forth'in claim .8 wherein said
phase-shiftingmeans .isran'element of ferromagnetic ma
terial of low conductivitytmagnetically biased transversely
Publication, Hogan: “The Microwave Gyrator,” Bell
System Technical Journal, vol. 31, No. l, January 1952.
to the axis of said one waveguide.
,
Kales, et al.: “A Nonreeiprocal Microwave Compo
.11, A selectivetransmission system for propagating 45 nent,” Journal of Applied Physics, vol. 24, No. 6, June
electromagnetic wave energy comprising tirst and second
1953, pages 816-17.